Modern people spend long periods of time continually sitting at our work places or homes and while traveling between these places. The human body is not physiologically suited to this inactivity. In earlier times mankind spent little time in static sitting positions and much time walking. Our bodies are not well evolved for continual sitting. The physiology of sitting for an average adult of 166 pounds weight applies this load to about a fifteen inch square area (225 sq. inches). If the seating surface could achieve a perfectly uniform distribution over this area the unit pressure would amount to 38 mmHg. The normal human capillary and small vein pressure is 11 to 33 mmHg. A seating contact pressure which exceeds the blood pressure causes the flow of blood, and therefore the supply of oxygen, to be blocked. In actual seats there are regions where the local sitting contact pressure is much higher than the local blood pressure resulting in more severe localized blockage. For short time periods (a few minutes) this blockage causes little discomfort and no physiological damage. However, after a prolonged period the reduction in blood flow results in the sensation of discomfort which eventually becomes severe. If blood flow is not restored, tissue death ensues. The sensation of discomfort prompts us to frequently relieve pressure and restore blood flow by adjusting our position during extended sitting or reclining situations.
Paralyzed humans do not sense discomfort or pain signals when normal blood flow is occluded and are in danger of developing pressure sores (decubitus ulcers) if they are not regularly repositioned. The same problem arises for many other bedridden patients.
Various attempts have been made to alleviate fatigue and other symptoms associated with prolonged inactivity on a chair or bed. Although the effects are very different, convalescing or paralyzed patients, equipment operators and office workers all suffer damage from the same fundamental cause. The supports (chairs or beds) on which they are at rest, place sufficient pressure on the contacted portion of their bodies that circulation is impaired, which denies tissue needed oxygen. The damage may range from discomfort to debuctus ulcers. The effect on an office worker may be restlessness and a need to frequently shift position while that on a bedridden patient may be life-threatening skin lesions.
These problems have led to a range of solutions from inflatable mattress segments to carefully designed office chairs designed to distribute pressure as uniformly as possible.
Passive cushions (seat and mattress constructions) have been developed to make sitting or reclining more comfortable by using soft cushion materials and careful contouring of the seat structure. These materials include foam plastic or elastomeric materials, encased gels, air filled cushions and refined spring and membrane support systems. Passive support systems, no matter how uniformly perfect the load distribution, will still block capillary blood flow because of the weight and contact surface areas of humans.
Prior art inflatable cushions either require active pressure inflation with no full-height reserve cushioning (for use in the absence of pump pressure) or, where passive or backup foam cushioning is provided in a vacuum-driven device, half of the surface area or less is available for cushioning when the vacuum chambers are collapsed (or pressure chambers deflated). Passive systems, especially those for seating surfaces, cannot prevent the closing off of capillaries. Even with perfect distribution of pressure, there is not enough surface area on the human posterior to support the body""s weight without cutting off blood flow which results in discomfort and, eventually, tissue damage. The same is true for localized areas on the bodies of paralyzed or otherwise bedridden patients. For example the heels of bedridden patients frequently develop bed sores.
Most prior art inflatable cushions have cells that are pressurized above atmospheric pressure by a pump and alternately collapsed by allowing the pressurized air to be exhausted. These devices provide no support when the pump is not operational. Prior cushions that incorporate inflatable cells combined with foam use the foam only when the pump is not operational. Therefore, air pressure and the power necessary to create it must do all the work of support when the system is active.
Vacuum or pressurized devices that provide inflation of, or collapsing of, cells in groups have typically provided no more than two or three groups of cells to be independently controlled. The failure to provide more precise control over multiple cells is attributable in part to the fact that manifolding in the past was inadequate to support more than a minimal number of groups of cells. In vacuum systems, any attempt to run vacuum hose between groups of cells or other inflatable/deflatable structures will normally result in a pinching or other cutoff of the vacuum tubing during deflation. Even where two or more groups of cells are deflated, the amount of vacuum-pumping power that is required to deflate a high percentage of the total cell count in a reasonable time is substantial and therefore both energy consumption and noise are a problem.
There have been active support systems developed for both bedridden and seated individuals. Devices that rely on suction to remove part of the support to allow tissue recovery have typically relied on an inactive foam portion to provide the sole support during the vacuum phase as in the PCT publication WO 86/02244 (Ophee). Devices that have taken the form of alternating pressure pad arrays are periodically inflated with compressed air or allowed to deflate under the weight of the user. One of the earliest alternating pressure pads is disclosed in U.S. Pat. No. 3,199,124, Grant. This mattress uses active, alternating pressure pads for the bedridden. The device inflates one half of the support surface at a time which results in doubling the contact pressure loading on the user relative to the same pad fully inflated and not being cycled. These mattresses are also at a disadvantage because they can only be used when inflated and operational; there is no cushioning support when inactive. Also, there is no protection from bottoming out of the cushion. Thus if the subject using the support can not be fully supported on the air cushion, the deflation of cells will have no effect of removing the pressure from the surface of the skin.
Some active seats have combined foam and inflatable tubing to create an alternating pressure pad with extra support. In U.S. Pat. No. 3,867,732, Morrell discloses a cushion which has a plurality of inflatable tubes on top of a foam cushion. There is support from the cushion even if the tubes are deflated. In U.S. Pat. No. 5,388,292, Stinson et al. disclose a mattress with inflatable bladders containing elongated foam members. With a supply of air pressure to the bladders, the foam mattress converts to an air mattress and the foam no longer carries the load of the user.
There are other examples of cushions which use foam encased bladders. Some are used to hold the cushion in a custom contoured form which is created by the user""s body, as in U.S. Pat. No. 6,012,188, Daniels.
In U.S. Pat. No. 5,797,155, Maier, one or more support chambers are filled with foam and a fluid such as air. The chambers are connected such that a pressure equilibrium is reached with flow of the fluid between the chambers.
There are also self-inflating air mattresses which contain foam for cushioning. Such air mattresses can be deflated and made compact by removing the air, collapsing the foam, and closing an air valve. They are reinflated when the mattress air valve is opened and the foam returns to original size. U.S. Pat. No. 4,025,974, Lea et al., discloses a self-inflating air mattress of this sort.
The combination foam and fluid bladders described above are all passive cushions, and are inadequate for reducing pressure on all surfaces of the skin.
Active cushions which incorporate foam are better at relieving pressure, but have a major disadvantage in their basic structure. They require air pressure to support the entire weight of the user while in operation. When sections of the seat are deflated, the inflated sections must take on the additional load and support all the weight to prevent the cushion from bottoming out. Because of this construction, the foam in the seat is not used at all for supporting the user. It is only utilized when the seat is nonoperational or if the air bladders are bottomed out while operating. In either case there is no way to relieve pressure in localized areas to below capillary pressure. Therefore, the cushion""s pressure-relieving objective is unattainable.
One method of providing pressure relief while utilizing foam as a support structure within the cushion, is to periodically remove sections of the support cushion from the surface of the user so that blood flow to these areas is periodically restored and the tissues reoxygenated. This method was used by O""Brien as disclosed in U.S. Pat. No. 4,644,593. A mattress is provided with a relief device underneath the cushion which is periodically, mechanically, drawn downward to remove the cushion from the surface of the user. U.S. Pat. No. 4,799,276, Kadish, also discloses a mattress with vertical displaceable supports. These supports are withdrawn when the pressure on the support from the user""s body reaches a maximum level. These systems are complex and require a substantial amount of power to operate and therefore produce high levels of noise.
Another attempt at providing pressure relief is disclosed in U.S. Pat. No. 5,983,428, Hannagan. This is an alternating pressure pad with three arrays of inflatable cells. The cells are inflated to support the user and periodically deflated to relieve pressure on the surface of the user. To decrease the time needed to deflate the cells and achieve a low pressure within the deflated cells, a means of suction, such as a vacuum pump is employed. This method of supporting the user still requires a sufficient air supply to support the entire weight of the user while operating. It is not a suitable cushion when non active because the air cells do not provide support when unpressurized. Therefore, it would be desirable to have a new and improved active cushioning structure formed of a matrix of four or more cells where multiple cells could be selectively deflated in a selected pattern, but where less than xc2xc of the cells were deflated at a time. The deflation of a minority fraction of the cells has the synergistic effect of reducing power consumption and noise and at the same time limiting the incremental increase in pressure on the rest of the supported body. It is desirable to have a device where the cells incorporate open-celled foam within the vacuum cell membranes which substantially completely cover the supporting structure to provide fully cushioned support in the absence of electrical power. Such a device is particularly desirable where the contact pressure is not increased by more than 25% during a cell group""s collapse. Such a device is inherently efficient because of the recovery of energy stored in the compressed foam. Additional energy efficiency can be achieved by cross-manifolding a cell being exhausted with one that is being refilled.
In accordance with an exemplary embodiment of the invention, the deficiencies of prior art designs are overcome in a cushioned support that incorporates both resilient passive cushioning and vacuum manifolding to multiple cells that encase the passive cushioning.
The object of this invention is to provide an active, human body support for safe, comfortable, long time, sitting or reclining that enables a continuously satisfactory level of tissue oxygen in all body contact regions without body movement by the user.
The embodiment features:
a) an upper body cushioning and support surface
b) a multiplicity of deformable support cells having an internal volume and that includes a void space filled with a fluid which in the present embodiment is air;
c) means to remove fluid on a cyclic basis from deformable support cells to cause their deflation and collapse; and
d) means to allow the fluid to return to deformable support cells to cause their inflation after a certain duration of time has elapsed in the collapsed position.
The exemplary apparatus provides excellent passive support when not activated (powered).
The support includes the following system components:
1) vacuum pump;
2) a manifold connecting each cell to the vacuum pump;
3) a valve system interposed between the valve and manifold with multiple parts for periodically connecting cells or groups of cells to the vacuum pump.
When activated, the apparatus continuously maintains adequate tissue oxygen level and comfort in all body contact regions without user effort.
The apparatus works in harmony with the physiological characteristics of the human body venous system response when subjected to local external surface forces in sitting or reclining positions.
The apparatus functions with minimum power consumption, noise and vibration making its presence known only by the absence of discomfort.